bpo-39674: Fix collections ABC deprecation notice (GH-25281)

The deprecation originally slated for 3.9 was deferred to 3.10
(bpo-39674, GH-18545) and the documentation on the 3.8 release was
updated accordingly (GH-18748). However the deprecation notice in
the code was left as is, and still indicates deprecation with 3.9.

Lib/collections/__init__.py

@@ -48,7 +48,7 @@ def __getattr__(name):
         import warnings
         warnings.warn("Using or importing the ABCs from 'collections' instead "
                       "of from 'collections.abc' is deprecated since Python 3.3, "
-                      "and in 3.9 it will stop working",
+                      "and in 3.10 it will stop working",
                       DeprecationWarning, stacklevel=2)
         globals()[name] = obj
         return obj